The present invention relates to a reflow method and reflow device wherein, by heating a printed circuit board on which electronic components are loaded and to which solder cream has been applied at locations to be connected, solder is melted and electronic components soldered.
A variety of methods for reflow soldering technology to mount electronic components on printed circuit boards are already known. These methods include, for example, batch reflow soldering of surface mount components, local soldering of insert mount components after batch reflow soldering of surface mount components, and local reflow soldering of surface mount components and insert mount components.
A conventional reflow device for batch reflow soldering of surface mount components is constituted so as to melt solder and to solder electronic components by uniformly heating a printed circuit board with the radiant heat of a panel heater and hot air heated to a prescribed temperature.
Also, the reflow device according to the report of Japanese Patent Publication No. 7-73790 is an example of a reflow device for local heating and reflow of surface mount components and insert mount components. As shown in FIG. 11, this reflow device (50) is equipped with the following: hot air chamber (53) installed on the lower side of the transport path (52) for the printed circuit board (51) which collects gas heated to a temperature at which solder cream melts, an upper plate (57) installed to cover the opening section (54) of the hot air chamber (53) and in which is formed a plurality of hot air blow holes (56) to blow the hot air (55) selectively on only the necessary sections of the printed circuit board (51), and means for transport (58) to supply and remove the printed circuit board (51).
Because heating is local, this reflow device (50) makes possible the following processes: sectional soldering, soldering of components with low heat resistance, and concurrent soldering of lead components (59) and chip components (60) wherein the lead terminals protrude from the lower surface of the board.
However, batch reflow soldering is not possible when using the aforementioned, conventional type of reflow device if electronic components with low heat resistance are present together on a printed circuit board. Those components with low heat resistance among the electronic components will be damaged if that printed circuit board undergoes batch reflow soldering with the reflow device; therefore, the components with low heat resistance among the electronic components must be soldered separately, resulting in the problem of decreased productivity of the mounting process.
Meanwhile, the reflow device (50) shown in FIG. 11 makes possible batch soldering for a printed circuit board (51) on which electronic components with low heat resistance are present together by locally blowing hot air without blowing the hot air to the locations of the electronic components with low heat resistance.
Actually, batch soldering of the electronic components (lead component (59) and chip component (60), etc.) placed on the entire surface of the printed circuit board (51) is not possible for the following reason. In effect, reflow soldering electronic components such as lead component (59) and chip component (60), etc., with the reflow device (50) requires heating to temperatures in the vicinity of 230xc2x0 C. for 20-30 seconds. Hot air of a temperature of roughly 350xc2x0 C. or greater is necessary to ensure the quantity of heat necessary for that purpose. In hot air of such high temperatures, areas of the printed circuit board (51) in which the temperature rises easily reach temperatures approaching that of the hot air. Even heat resistant components (for example, the temperature of heat resistance for QFP is 250xc2x0 C. (QFP is heat resistant to temperatures of 250xc2x0 C.) cannot withstand that temperature. When the hot air temperature is reduced to 250xc2x0 C., the temperature of heat resistance, in order to avoid [damage], the risk is that areas of the printed circuit board (51) in which the temperature rises with difficulty are not heated to the temperatures necessary for soldering within a prescribed period of time and high reliability soldering may not result.
An object of the present invention is to provide a reflow method and reflow device which resolve the problems and make possible batch soldering with high reliability and without resulting in heat damage to electronic components on the printed circuit board.
In order to solve the problems, the reflow method of the present invention is a reflow soldering method in which hot air is blown locally and roughly perpendicular to locations to be connected on one surface of a printed circuit board, concurrent with radiant heating of the surface of a printed circuit board, on which electronic components are loaded and to which solder cream has been applied at locations to be connected.
This reflow method permits secure soldering in such a manner that the temperature of the hot air does not exceed the temperature of heat resistance of the electronic components because of its combination with the radiant heat. Moreover, this reflow method can permit soldering in such a manner that only those points to be connected are heated selectively because the hot air is blown locally and roughly perpendicular to the points to be connected. This reflow method prevents heat damage to sections other than the points to be connected and ensures that the solder at the points to be connected is melted.
Additionally, the reflow method of the present invention permits batch reflow soldering of electronic components, on a printed circuit board to which solder cream is applied, because the surface to undergo reflow soldering of the printed circuit board is heated while the components with low heat resistance, among the electronic components on the printed circuit board, are cooled.
Since reflow soldering is performed while the components with low heat resistance among the electronic components are cooled, this reflow method can prevent damage to the components with low heat resistance among the electronic components and can perform batch reflow soldering of electronic components on a printed circuit board. Consequently, performing reflow soldering for operations conducted with conventional flow dip soldering improves soldering quality. In effect, the flow method results in a two-time heat history since the printed circuit board passes through the flow device after passing through a curing oven in order for temporary affixation of surface mount components with adhesive. However, in the method of the present invention, the board needs to only pass once through the reflow device. This results in a one time heat history and prevents deterioration of the capacity of the electronic components. Also, when surface mount electronic components are placed on both surfaces of the printed circuit board, points to be connected of the electronic components on the lower surface are cooled during reflow; therefore, those electronic components will not drop off even if they are not affixed with adhesive. Consequently, the process for applying adhesive when the surface mount electronic components are placed thereon can be eliminated.
Also, in the aforementioned reflow method, the electronic components placed on the printed circuit board include surface mount components and insert mount components. The present invention permits batch reflow soldering of these surface mount components and insert mount components.
This reflow method makes possible reflow soldering of lead insert mount components which before now could not pass through a reflow device which heats the entire board. Consequently, production costs do not rise because insert mount components can be used without further processing.
Also, in the aforementioned reflow method, the present invention heats one surface of the printed circuit board while cooling the other surface of the printed circuit board.
With this reflow method, reflow soldering can be performed without impediment even if components with low heat resistance are on the other side.
The reflow device of the present invention has the following placed together in a heating section: means for radiant heating, for radiant heating of one surface of the printed circuit board, to which solder cream is applied at points to be connected and on which electronic components are placed; and means for hot air heating, to blow hot air locally and in a direction roughly perpendicular to the points to be connected on one surface of the printed circuit board, which is being heated by that means for radiant heating.
This reflow device can put into practice the aforementioned reflow method by supplying a printed circuit board to the heating section because the following are placed together in the heating section: means for radiant heating, for radiant heating of one surface of the printed circuit board, and means for hot air heating, to blow hot air locally and roughly perpendicular to the points to be connected on that surface of the printed circuit board.
Additionally, the present invention is that in which means for hot air heating is constituted of a hot air header forming a flat space touching the surface of the panel heater on the side of the printed circuit board and in which is located a mask plate, in which are formed blow holes corresponding to the points to be connected on the surface in opposition to the printed circuit board; and means for supplying hot air, to supply the hot air to within the hot air header from the side section thereof, in the aforementioned reflow device.
With this reflow device, radiant heat from means for radiant heating is definitely radiated through the hot air header to the printed circuit board, while hot air is definitely blown from the mask plate locally and roughly perpendicular to the points to be connected.
Also, the present invention is constituted in such a manner that, in the aforementioned reflow device, a dispersion plate in which a plurality of through holes are dispersed is placed with space between [itself and] the mask plate inside the hot air header and hot air is supplied from means for supplying hot air into the space between means for radiant heating and the dispersion plate.
With this reflow device, a flow of hot air inside the hot air header is homogenized with the dispersion plate, ensuring that the hot air is blown uniformly and appropriately against and roughly perpendicular to the points to be connected.
Also, in the aforementioned reflow device, a black body paint coating is made on the mask plate; therefore, the present invention can improve the quantity of radiant heat with this reflow device.
Also, means for cooling to blow cool air to prescribed locations of the other surface of the printed circuit board, one surface of which is being heated with means for radiant heating and means for hot air heating, is installed in the aforementioned reflow device; therefore, the present invention can contribute to the operation by blowing the cool air as mentioned above.
Also, the aforementioned reflow device is equipped with means for transporting, to transport the printed circuit board in the heating section, and lifting means for lifting and lowering boards, to lift the printed circuit board in the heating section to a prescribed heating position; therefore, the present invention can provide heating quickly and with good precision by lifting the printed circuit board to a heating position with this reflow device.
Also, the aforementioned reflow device has means for cooling installed in lifting means for lifting and lowering boards; therefore, the present invention can appropriately cool prescribed locations on the other surface of a printed circuit board with this reflow device.
Also, the aforementioned reflow device has an isolation plate to isolate the cooling atmosphere and the heating atmosphere surrounding the periphery of the printed circuit board, which is lifted to a prescribed heating position by lifting means for lifting and lowering boards; therefore, the present invention can heat and cool efficiently and with good precision and without intermixing of the cool air and hot air.
Also, the reflow device of the present invention is equipped with a heating section, to heat with means for heating a printed circuit board on which electronic components are placed, and a cooling section, to cool with means for cooling components with low heat resistance among the electronic components on the printed circuit board, which is being heated in the heating section.
Because reflow soldering during cooling of components with low heat resistance among the electronic components is possible, this constitution can prevent damage to components with low heat resistance among the electronic components and perform batch reflow soldering of electronic components on the printed circuit board.
Also, the present invention has means for transporting, to transport a printed circuit board in the heating section, installed in the aforementioned reflow device and means for cooling, arranged freely within a proximate space with respect to a printed circuit board which is transported in the heating section.
With this constitution, means for cooling can come to a proximate position as necessary and perform the cooling action at an appropriate position; at the same time, obstruction of the transport action by means for cooling can be avoided.
Also, in the present invention, the aforementioned reflow device is equipped with the following as means for heating of the heating section: a radiant heating element, such as a panel heater, for radiant heating of the printed circuit board and a hot air producing element for convection heating of a printed circuit board.
This constitution makes possible more appropriate heating of the printed circuit board. Basically, when the body of a lead insert mount component is cooled, a large quantity of the heat for heating the lead solder section is lost from the cooled body portion due to heat conduction. Consequently, this large quantity of lost heat and heat to raise the temperature of the lead solder section to nearly 200xc2x0 C., greater than the solder melting temperature (183xc2x0 C. for eutectic solder), must be supplied with a set amount of time (for example, approx. 20-30 seconds of the main reflow heating time). Here, in the case of using hot air as means of supplying heat, means to raise the temperature of the hot air or to accelerate the speed at which the hot air strikes the solder section is used in order to supply a large quantity of thermal energy in a short period of time. Because lead insert mounted components and surface mounted components are arranged on the heated surface of the printed circuit board by means of solder cream, means of accelerating the speed of the hot air is not used in consideration of the possible displacement of surface mounted components. In the case of using means to raise the temperature of the hot air, it is necessary that the temperature of the hot air be in the vicinity of 350xc2x0 C. However, the lead insert components and surface mount components are arranged on the heated surface of a printed circuit board; hot air at a high temperature will heat the surface mount components, which are not subject to cooling, to a temperature greater than their temperature of heat resistance and destroy them. Therefore, a panel heater to generate infrared rays, which are radiant heat, is used as means to supply heat. The temperature of the panel heater may be increased in order to supply a large quantity of thermal energy in a short period of time.
Also, in the present invention, the aforementioned reflow device is constituted to heat one surface of a printed circuit board with means for heating of a heating section and cool the other surface of the printed circuit board with means for cooling of a cooling section. A plate, to prevent the intermixing of the heated atmosphere of the heating section and the cooled atmosphere of the cooling section, which surrounds the printed circuit board is arranged roughly parallel to the board transport surface in the aforementioned reflow device.
This constitution prevents the intermixing of the heated atmosphere of the heating section and the cooled atmosphere of the cooling section.
Also, in the present invention, the following are arranged above the board transport surface in the aforementioned reflow device: a plate to prevent intermixture of the heating-cooling temperatures, having a punched hole of a size greater than that of the exterior dimensions of the board; a board stopping mechanism, to stop a printed circuit board at a prescribed position relative to the aforementioned punched hole; and a mechanism to lift and lower a board, to lift a board to a height in contact with or near the aforementioned plate, to prevent intermixture of the heating-cooling temperatures.
This constitution can satisfactorily lift a printed circuit board from a board transport surface to a height in contact with or near the aforementioned plate to prevent intermixture of the heating-cooling temperatures and can more surely prevent the intermixture of the heated atmosphere of the heating section and the cooled atmosphere of the cooling section.
Also, the present invention has a cool air blowing structure, for local cooling of the components with low heat resistance mounted on a printed circuit board, installed on the mechanism to lift and lower a board in the aforementioned reflow device.
This constitution can allow for cooled locations to be made appropriate, because the cool air is blown corresponding to the arrangement of the components with low heat resistance on the printed circuit board.
Also, in the present invention, holes, corresponding to the arrangement of components with low heat resistance on a printed circuit board, are made in a plate as a cool air blowing structure in the aforementioned reflow device.
This constitution can allow for cooled locations to be made appropriate, as cool air is blown appropriately from the holes, as a cool air blowing structure, on components with low heat resistance on a printed circuit board.
Also, in the present invention, a nozzle to adjust the distance from the cooled sections of a printed circuit board is installed in the aforementioned reflow device.
This constitution can allow for cooled locations to be made appropriate, because the constitution can more appropriately realize a cool air blowing structure corresponding to the arrangement of components with low heat resistance on a printed circuit board.
Also, in the present invention, the aforementioned reflow device has blow holes, made in a metal or resin block, as a cool air blowing structure; therein, the carving of the block adjusts the cool air blowing distance in accord with the height of the insert mount components.
This constitution can allow for cooled locations to be made appropriate, because the constitution can more appropriately realize a cool air blowing structure corresponding to the arrangement of components with low heat resistance on a printed circuit board.
Also, in the present invention, the aforementioned reflow device is equipped with a heating section, consisting of a preheating section and a main heating section, to heat a printed circuit board on which electronic components are placed and a transport section, to transport a printed circuit board. The following are installed in that preheating section: a heat source to preheat a reflow soldering surface, being one surface of a printed circuit board (the upper surface, for example); an exhaust duct to exhaust, in a direction roughly parallel to the printed circuit board and roughly at right angles to the direction of transport, the atmosphere of the other surface (the lower surface, for example) of a printed circuit board, which is especially not to undergo forced heating; and an external air intake placed on the other side of the aforementioned printed circuit board, for example, below the board transport surface, to maintain this other surface at a low temperature.
This constitution can maintain the atmospheric temperature of the lower surface of a board at about room temperature and can heat the upper surface of a board, while maintaining the bodies of insert mount components at a low temperature.